MipsTargetObjectFile.cpp revision e7338cd550a4ccde6796d2987b482ea9f0e239ef 
1//===-- MipsTargetObjectFile.cpp - Mips Object Files ----------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "MipsTargetObjectFile.h"
11#include "MipsSubtarget.h"
12#include "llvm/DerivedTypes.h"
13#include "llvm/GlobalVariable.h"
14#include "llvm/MC/MCContext.h"
15#include "llvm/MC/MCSectionELF.h"
16#include "llvm/Target/TargetData.h"
17#include "llvm/Target/TargetMachine.h"
18#include "llvm/Support/CommandLine.h"
19#include "llvm/Support/ELF.h"
20using namespace llvm;
21
22static cl::opt<unsigned>
23SSThreshold("mips-ssection-threshold", cl::Hidden,
24            cl::desc("Small data and bss section threshold size (default=8)"),
25            cl::init(8));
26
27void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
28  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
29
30  SmallDataSection =
31    getContext().getELFSection(".sdata", ELF::SHT_PROGBITS,
32                               ELF::SHF_WRITE |ELF::SHF_ALLOC,
33                               SectionKind::getDataRel());
34
35  SmallBSSSection =
36    getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
37                               ELF::SHF_WRITE |ELF::SHF_ALLOC,
38                               SectionKind::getBSS());
39
40}
41
42// A address must be loaded from a small section if its size is less than the
43// small section size threshold. Data in this section must be addressed using
44// gp_rel operator.
45static bool IsInSmallSection(uint64_t Size) {
46  return Size > 0 && Size <= SSThreshold;
47}
48
49bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
50                                                const TargetMachine &TM) const {
51  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
52    return false;
53
54  return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
55}
56
57/// IsGlobalInSmallSection - Return true if this global address should be
58/// placed into small data/bss section.
59bool MipsTargetObjectFile::
60IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
61                       SectionKind Kind) const {
62
63  const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
64
65  // Return if small section is not available.
66  if (!Subtarget.useSmallSection())
67    return false;
68
69  // Only global variables, not functions.
70  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
71  if (!GVA)
72    return false;
73
74  // We can only do this for datarel or BSS objects for now.
75  if (!Kind.isBSS() && !Kind.isDataRel())
76    return false;
77
78  // If this is a internal constant string, there is a special
79  // section for it, but not in small data/bss.
80  if (Kind.isMergeable1ByteCString())
81    return false;
82
83  Type *Ty = GV->getType()->getElementType();
84  return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
85}
86
87
88
89const MCSection *MipsTargetObjectFile::
90SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
91                       Mangler *Mang, const TargetMachine &TM) const {
92  // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
93  // sections?
94
95  // Handle Small Section classification here.
96  if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
97    return SmallBSSSection;
98  if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
99    return SmallDataSection;
100
101  // Otherwise, we work the same as ELF.
102  return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
103}
104